KANO, Nigeria — Attackers armed with bombs and guns opened fire at church services at a Nigerian university on Sunday, killing around 20 people as worshippers tried to flee, witnesses and officials said.

Explosions and gunfire rocked Bayero University in the northern city of Kano, with witnesses reporting that two church services were targeted as they were being held on campus.

One of the services was being held outdoors, while the second was inside a building, but with an overflow audience outside, witnesses said.

Officials were unable to confirm casualty figures, but an AFP correspondent counted six bullet-riddled bodies near one of the two sites.

At least another dozen bodies could be seen on a roadside by the university, but the exact number was unclear.

Musical instruments and half-eaten meals could be seen at the site of one of the services.